1. Field
The disclosed subject matter relates to a vehicle damper and a method of manufacturing the same. More specifically, the disclosed subject matter relates to a rod guide and sealing structure for a vehicle damper and the sealing method therefore.
2. Brief Description of the Related Art
Vehicle dampers are used in conjunction with vehicle suspension systems to absorb unwanted vibrations which occur during operation of the vehicle. In order to absorb this unwanted vibration, vehicle dampers are connected between the sprung mass (the body) and the unsprung mass (the suspension system) of the vehicle. A piston is located within a pressure tube of the vehicle damper and is connected to either the sprung mass or possibly the unsprung mass of the vehicle. The pressure tube is connected to the other of the unsprung mass or sprung mass of the vehicle and is filled with hydraulic fluid. Because the piston has the capability of limiting the flow of hydraulic fluid within the pressure tube when the vehicle damper is compressed or extended, the vehicle damper is able to produce a damping force which counteracts the vibrations which would otherwise be transmitted from the suspension (unsprung mass) to the body (sprung mass) of the vehicle.
A conventional dual tube vehicle damper includes a pressure tube with a piston disposed therein and a reserve tube surrounding the pressure tube. A piston rod is connected to the piston and extends through the upper end of the pressure and reserve tubes. At the lower end of the pressure tube, a base valve is located between the pressure tube and the reserve tube. The base valve controls fluid flow between the working chamber defined by the pressure tube and the reserve chamber defined by the reserve tube. The damping force is created by restricting the flow of fluid through passages in the piston and valve plates which regulate passage of fluid between opposite sides of the piston within the working chamber.
Because the piston rod is located on only one side of the piston, a different amount of fluid is displaced on the compression stroke as opposed to the rebound stroke. The difference in the amount of fluid is termed the rod volume. The rod volume of fluid is pushed out of the pressure tube, through the base valve and into the reserve tube during a compression stroke. During a rebound stroke, the rod volume of fluid flows in the opposite direction from the reserve tube, through the base valve and into the pressure tube.
The piston rod is supported at its lower end by the piston and is slidingly received at the upper end of the vehicle damper by a rod guide. The rod guide thus functions as a slide bearing for the rod. The rod guide properly positions the piston rod within the pressure tube and also acts as a closure member for both the pressure tube and the reserve tube. A small clearance can be formed between the inner periphery of the bearing portion of the rod guide and the outer periphery of the piston rod in order to provide smooth sliding of the piston rod through the rod guide. The small clearance also allows for the hydraulic fluid to lubricate the interface between the piston rod and the rod guide.
In addition to locating the piston rod and closing the pressure and reserve tubes, the rod guide supports and locates a seal assembly which is designed to keep the hydraulic fluid within the vehicle damper and also keep contaminants out of the vehicle damper. The seal assembly normally interfaces between the reserve tube and the rod guide, between the rod guide and the piston rod and possibly between the reserve tube and the piston rod. The seal assembly is designed to keep hydraulic fluid within the vehicle damper as well as keep dirt and other contaminates from entering the vehicle damper. The dirt and contaminants can be present and can adhere to the exposed portion of the piston rod.
There have been numerous seal systems designed and developed for meeting the difficult environmental and sealing requirements for vehicle dampers. While these conventional art seal systems are adequate for their intended purpose, the continued development of vehicle dampers and related seal systems has been directed towards dampers that are made of different materials and have different constructions, requiring different types of seals and seal systems.
One type of vehicle damper and seal system that is currently under continuous development is a monotube type damper. In a monotube type damper, a second reserve tube is not necessary. Instead, a second “floating piston” is provided within the first tube and is located below the working piston. The floating piston divides a working chamber of the monotube that is filled with hydraulic fluid from a lower chamber that can be filled with gas or other easily expandable/contractible fluid. The working piston is connected to a piston rod and moves with respect to the monotube structure by passing through a sealing structure/system located at an upper end of the working chamber above the working piston, similar to the system described above with respect to a dual chamber damper.
A typical monotube damper seal system is shown in FIG. 2A in which a seal system includes an aluminum rod guide 910 connected to an end of a single steel tube 972. The outer portion of the rod guide 910 is sealed with a surface of the inner tube wall 972b by O-rings 917 that prevent hydraulic fluid 902 from escaping. Likewise, the inner through hole 911 of the rod guide is sealed at the juncture between the rod guide 910 and the piston rod 941 by a lower inner seal 930. A lock ring 936 is press fit into an opening in the lower surface 915 of the rod guide 910 to lock the lower inner seal 930 to the rod guide 910. The rod guide 910 can be locked with respect to the tube 972 via a clinch ring indent in the tube 972 that corresponds to an indent in the rod guide 910.
The top surface 912 of the rod guide 910 is surrounded by a wall of the bordering tube 972 that extends beyond the rod guide 910 and forms a cup with the top surface 912 of the rod guide. This “cup” shaped portion tends to trap water 980 and other dirt and debris 981 at the top of the rod guide 910.
As shown in FIG. 3, the water 980 and debris 981 that are trapped by the tube wall 972 and rod guide 910 at the top of the damper 900 can result in a break down of the seal system between the rod guide 910 and either the tube 972 or the piston rod 941. The break down occurs when the water 980 and/or debris 981 get in between either the piston rod 941 and rod guide 910 or the rod guide 910 and inner surface 972b of the tube 972. The water 980 and/or debris 981 cause the O-ring(s) 917 and/or lower inner seal 930 to deteriorate, resulting in water, debris or hydraulic fluid either entering into the working piston chamber or escaping from the working piston chamber. Over time, this defect can cause deterioration of performance in the damper 900 and possibly failure of the damper 900.
In some monotube dampers the rod guide 910 is made from aluminum (that can be anodized) while the tube 972 is made from steel (which can be galvanized). Thus, at the juncture between these two structures, galvanic corrosion can also occur, which can cause poor performance or failure of the damper sealing system. For example, galvanic corrosion between the rod guide and the piston rod or between rod guide and the damper tube can result in free play and relative movement between the parts, causing unwanted noise and further deterioration and loss of structural integrity for the damper 900.
Thus, there has been a long felt need to improve the sealing system in monotube and other types of dampers, to avoid corrosion and deterioration of the seal system, to improve or broaden the tolerance requirements for the parts that make up dampers, and to improve the overall performance and manufacturability of dampers in general.